Telephone system



am IIFEL m wt m N Rm 653 w NM 62a E33 3% m2: 6 m mum R. E wt c. E. LOMAX TELEPHONE SYSTEM Filed 066. 28, 1955 2 Sheets-Sheet 1 April 13, 1937.

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CLARENCE E. LOMAX ATTORNEY.

6 h H 5 6 v W 6 m NQ Q n H 5 3 2 6. 3 Cu 6 n Patented Apr. 13, 15337 UNITED STATES amass PATET OFFICE TELEPHONE SYSTEM Application October 28, 1935, Serial No. 47,127

3 Claims.

The present invention relates to telephone systems in general, but is concerned more particularly with telephone systems wherein a line use-d for telephone purposes is used also for the trans- 5 mission of telegraph messages. The object of the invention is the production of new and improved circuit arrangements Which enable a pair of conductors to serve as a metallic subscriber telephone line and as a ground-return telegraph 10 line without mutual interference when the line is used for telephone and telegraph purposes at the same time.

General description 15 It has been chosen to illustrate the invention as applied to a subscriber line of considerable length, composited to provide two ground-return telegraph channels in addition to the metallic telephone channel, with one telegraph chan- 20 nel used for the transmission of telegraph messages and the other telegraph channel used for the transmission of ringing current and signal ling current incidental to the use of the line for telephone purposes. Since the impulses gener- 25 ated by the calling device in an automatic telephone system may be transmitted over the telegraph channel assigned to the use of the telephone subscribers, it has been chosen to illustrate the invention as applied to an automatic 30 telephone system.

A feature of the invention is that the exchange apparatus is permitted to remain unchanged as regards the setting up of connections between standard lines, while a repeater is pro- 35 vided individual to the combination telephone and telegraph line, to provide for the transmission of ringing current over the llne when the line is called and for the transmission of switchhook and calling-device signals from the telephone substation to the switchboard apparatus.

One situation in which'the invention is particularly useful is encountered in privately owned railroad exchanges. Certain railroad telephone 4 lines extend many miles from the exchange to a telephone substation, with the result that a considerable economic gain is realized if the pair of conductors can be used to furnish telegraph service in addition to telephone service.

Referring now to the drawings, comprising Figs. 1 to 3, they show the invention applied to a line of a l00-line automatic telephone system. Figs. 1 and 2 show equipment involved in the handling of both telephone and telegraph traffic 55 over the subscriber line L, while Fig. 3 shows a desirable modification of the repeater RI, Fig. 2, providing automatic intermittent ringing.

In Figs. 1 and 2, the telephone line L, comprising conductors I2I and I22, extends between the repeating coil RCI, located adjacent the telephone substation B, and the repeating coil RC2, located in the telephone exchange. The substation B is a local-battery automatic substation, suitably modified to permit ringing and signalling over the separate conductor III, while conversation is carried on over conductors I03'and In the telephone exchange, Fig. 2, the repeater RI is interposed between the repeating coil RC2 and the exchange apparatus for the purpose of repeating the signal impulses atthe uppercontacts of line relay 221 and of controlling the application of ringing current over the associated one of the two telegraph channels to signal the subscriber at substation B.

Through its terminals 2| I, the repeater RI is connected with the individual lineswitch LS2. Fig. 2 shows also the line of telephone substation A, having the individual lineswitch LSI. lineswitches LSI and LS2 have common access to a group of connectors, of which the connector C is one. This connector has access to all of the lines entering the exchange through groups of terminals such as those indicated as individual to the respective illustrated lines. 0f the lineswitches LS! and LS2 and the connector C, only the Wipers and illustrated bank terminals are shown, as the circuits and mechanisms of these switches are well understood.

The telegraph substation TSI, Fig. 1, and the telegraph substation T82, Fig. 2, are shown as of the Morse, key-and-sounder type.

Condensers I05 and 201 associated with the line windings of the repeating coils ROI and RC2 isolate the conductors I2I and I22 from each other as regards direct current, thereby preventing direct-current interference between the two telegraph channels. The differentially connected retard coils I06, I07, MI, and 202 are provided to avoid grounding of conductors I2I and I22 as regards the voice currents impressed on these conductors during conversation and also to provide the required gradual current change in the line conductor to prevent signal noisesfrom being superimposed on the telephone circuit. The condensers I08, I09, 203, and 204 are paired with the respective coils I06, I01, MI, and 202 in.iur therance of the arrangement for preventing sharp voltage fluctuations occasioned by telegraph signalling. It will be understood, of course,

The

that while the coils such as I06 and I0! are each differentially wound so that they are substantially non-inductive to the relatively gradual changes in current flow that take place in signalling over a telegraph channel, they are highly inductive to the relatively rapid changes that take place in voice-current transmission, because of the leakage magnetic return path through the air for each of the coils of the pair independent of the other. 7

It is to be understood, of 7 course, that the compositing arrangement for deriving the telegraph channels herein disclosed is merely illustrative, and that any suitable well-known method of deriving the low-frequency telegraph channels may be used.

Detailed description The disclosure having been described generally,

the substation A is a standard two-wire automatic substation.

Call from substation A to substation B When the receiver is removed; at substation A, the lineswitch LSI operates in the usual manner to search for an idle connector. Assuming that the connector C is the first one found to be idle,

' this connector is seized through the wipers of thelineswitch LSI, when they come to rest in engagement with the terminals of the connector C. The connector C is thereupon prepared for operation in theusual manner. 7

When. the subscriber at substation A dials the manner. Assuming that the line is idle, connec- 7 tion is made therewith and theconnector C aps of. a circuit through contacts of relay 222 of the plies ringing current in the usual manner. The ringing current, however, is not permitted to reach the line L, because of the open connection at the upper contacts of line relay 22!.

Ground potential is applied byway of the C wiper ofthe connector C to the 'C, lead of the called line for the purpose of energizing the cutoiT relay (not shown) of the lineswitch LS2 to thereby disconnect the usual line relay of the lineswitch. This ground potential is. also effective to guard the called line from further seizure by another of the connectors. V

The application of ground potential to the C lead of the called line results also in the closure repeater RI for the associated cut-01f relay 223 in the repeater. Relay 223 operates to disconnect the incoming line relay 22! of the repeater from the associated telegraph lead 206'. The lead 206 is also extended by the upper armature of cutoff relay 233', through contacts of the normally en-ergized-ring-0ut-Off relay 224, to the generator lead 232 associated with the ringing-current.

transformer 23L Ringing current from lead 232 now passes to the ringer -l0l of substation B through contacts of cut-off relay 223 and thence over the telegraph channel including retard coils 202 and I06, and conductor III. in series with ringer I0l normally prevents direct current from flowing over the associated teleing through the associated condenser, to signal the subscriber at substation B.

As a further result of the energization of cutoil relay 223, the normally existing circuit for ring-cut-oif relay 224 is broken. Relay 224, as is indicated by the solid-black upper portion thereof, is equipped witha copper collar on the armature end thereof so as to render the relay slow-acting. As a result relay 224 delays somewhat in restoring after'i-tscircuit is opened. When it does restore, relay 224 disconnects ringing lead 232 to terminate the splash application of ringing current, and at its upper contacts it reconnects line relay 22I to the lead 206.

When the subscriber at substation B responds to the operation of the ringer I0l brought about as above described, the removal of the receiver R permits the switchhook spring-combination I02 to move to alternate position. The local circuit is closed through the transmitter T and the primary winding of the induction coil IC; the receiver R is bridged across the talking conductors I03 and I04 in series-with the secondary winding of the induction coil IC; and the telegraph conductor 1H is disconnected from the ringer I0! and is extended to ground through the normally closed impulsing contacts of the calling device CD. The substation B is thereby prepared for conversation, and a current flow is established over conductor Ill and through retard coils I06 and 202, upper contacts of the now-restored ring-cut-ofi relay 224 and through the winding of line relay 22! to the negative pole of theex change battery. Relay 22i energizes over this circuit and at its inner armature closes a circuit for hold relay 222., Hold relay 222 operates and disconnects cut-off relay 223, atthe same time looking itself to the C lead of the lineswitch LS2 and of the connector C, which looked condition is maintained until the connection is broken down. Cut-off relay 223, being disconnected by hold relay 222, nowrestores and. connects line relay 22l to conductor 206' at another point, at the same time opening an additional point in the previously established ringing circuit and closing a reoperating circuit for ring-cut-ofi relay 224;

Relay 224 now reoperates preparatory to timing the application of ringing current on the next call received. a

At its upper contacts, line relay 22| closes a loop across the associated negative and positive talking conductors and the right-hand windings of repeating coil 209. the resistance characteristics of a subscribed line of optimum value, while condenser 209 bypasses voice currents around the resistor 208 In the connector C,'the usual ring-cut-ofl operation and the operation of the usual back-bridge or battery-feed relay now take place responsive to the current flow through the upper contacts of the line relay 32 l. The connector C is thereby brought into talking condition topermit conversation between the substations A and B over the outlined heavy talking conductors.

The condenser I The resistor 208 simulates I At the end of the conversation, when the subscriber at substation B replaces his receiver, line relay 22I restores when it is reconnected in circuit with the ringer IOI and associated condenser. Upon restoring, line relay 22I opens the initial circuit of holding relay 222, but relay 222 remains operated and locked to the associated C conductor for the time being. At its upper contacts, line relay 22I opens the back-bridge circuit through the connector C and permits the back-bridge relay (not shown) of the connector C to restore for whatever purpose desired.

When the subscriber at substation A replaces his receiver, the connection established through the lineswitch LSI and the connectorC is broken down in the usual manner, and the connector C is restored to the normal position.

Call from substation B to substation A Assuming now that he desires to converse with the subscriber at substation A, the subscriber at substation B removes his receiver R and then turns the calling device CD in accordance with the digits in the number of substation A. Upon the removal of the receiver, the receiver R and the transmitter T are connected in circuit at hookswitch contacts I02, as before, and the telegraph lead III is switched over from ringer IDI to the impulse contacts of the calling device CD. When this occurs, line relay 22I of the repeater RI becomes operated over the associated telegraph circuit.

Upon operating, line relay 22I operates hold relay 222 to disconnect cut-off relay 223 and to prepare a locking circuit for the upper winding of relay 222, whereby operation of relays 223 and 224 responsive to the placing of ground potential on the C lead is prevented.

At its upper contacts, line relay 22I closes a circuit over the associated talking conductors and through the resistor 208 and right-hand windings of repeating coil RC2 for the line relay (not shown) of the lineswitch LS2. By this operation, the lineswitch LS2 is caused to search for an idle connector, and ground potential is returned on the associated C lead to guard the calling line against seizure by a connector. This grounding operation closes a locking circuit for the upper winding of relay 222. It may be assumed that the lineswitch LS2 extends connection to the connector C, in which event the connector C is prepared for operation in the usual manner.

When the calling device CD is operated, the upper contacts thereof (off-normal shunt contacts) shunt the receiver R to' by-pass disturbances created at'the upper contacts of relay 22!.

Responsive to the dialling of the digits in the number of the line. of substation A, line relay 22I restores each time its circuit is opened, and each time it does so it breaks the impulse circuit at its upper contacts to cause the connector C to be operated under control of its line relay in the usual manner. Relay 222 is held operated and does not restore responsive to the dialling operation because it is held looked over the associated C lead.

The connector C is caused to raise its wipers opposite the desired level of bank contacts when the first digit is dialled and it brings its wipers into engagement with the illustrated terminals of the line of substation A when the second digit is dialled. Ringing current is applied to the line of substation A in the usual manner, and the ringing operation is automatically terminated when the subscriber at the called substation responds.

Conversation may now proceed as desired. When the conversation is ended, the subscriber at substation A replaces his receiver, but the connection remains established until the subscriber at substation B replaces his receiver and permits line relay 22I to restore and open'the control circuit of the connector C at its upper contacts. The restoration of the usual slow-acting release relay (not shown) of the connector C permits the connector C to restore to normal condition, and permits the clearing out operation to be performed at the lineswitch LS2, responsive to removal of ground potential from the C lead. Relay 222 of the repeater RI restores responsive to the said ungrounding of the associated C lead, returning the repeater RI to the normal condition indicated in the drawings.

It is to be noted that the common-connection symbols are shown associated with leads I63, I M, and II I,. extending to substation B. These common-connection symbols indicate that these three leads may be common to two or more substations, whereby a call transmitted to the line L may be received at any one of these substations, or a call may be originated over any one of these substations in the manner described inconnection with the operation of originating a call from substation B.

Regarding the telegraphing from telegraph station TSI to station TS2, this telegraphing is carried out in the usual manner by opening and closing the circuit at either of the keys, and the current changes produced thereby in line I22 and the accompanying voltage changes on conductor I22 with respect to conductor I 2I are prevented from telephonically influencing conversation being carried on over the line L by the illustrated retard coils and by-pass condensers, as previously described. 1

The modified repeater R2 trolled, in contrast to the ring-cut-ofi relay 22s and the way it is controlled. In the system as illustrated in Figs. 1 and 2, only a single, measured application of ringing current is made to the called line. In Fig. 3, the ring-cut-oif relay 324 is arranged to operate responsive to current 1 flow which takes place over the called line when the receiver is removed thereat, for which reason the ringing operation may proceed until the called subscriber replies. The ringing-interrupter relay 333 is operated intermittently in the usual manner in order to cause the application of ringing current to be intermittent instead of continuous. The operation of the repeater R2 will now be described briefly from the standpoint of the reception of a call for the associated line.

Assuming that the repeater R2 is substituted for the repeater RI, the grounding of the associated. C lead when a call is received through a connector such as the connector C results in the operation of cut-01f relay 323 to disconnect the telegraph conductor from line relay 32I and extend it through contacts of ring-cut-off relay 324 to the intermittent ringing lead 332. The ringcut-01f relay 324 is of the usual construction of i a ring-trip relay, having a copper collar around the armature end thereof; and-1a :copper sleeve under the winding space, both of which contribute successively; Relay 322, in addition to closing its to slow up thejmagnetic responseof the-relay sufiiciently to prevent its operation from the ringing current passing through its, lower winding. The relay operates from the continuous flow of current through its lower winding from the negative pole of the exchange battery when the called subscriber replies. The upper winding of the relay is then included in a locking circuit through the inner, upper contacts of the relay, to ground over the C lead; The ringing circuit is opened at the middle armature of the relay, while the line relay 32I is-reconnectedat the upper armature.

Line andrhold relays 32l and 322 now operate own locking circuit, breaksthe holding'circuit of relay 323 andthe locking circuit of relay*324.

Quick-actingcut-ofi relay,323 restores immediaterectly toground.v The terminals 2 of the repeater RI are connected to the ring, tip, and sleeve conductors, respectively, of the manual. switchboard, while the current-supply connections to the upper winding of relay 222 and to the winding of 223 are made to" agree with the alteration of potential on the sleeve" conductor of the manual 'line circuit when a plug is in the jack, as com- ,pared with the potential that normally exists thereon. The usual manual common battery signalling is thenaccomplished at the upper contacts of line relay 22I, while relays 222 and 223 are controlled over the sleeve conductor in the manner described in connection with their control over the illustrated C conductor.

What is claimed is:

1. In combination, a telephone exchange and a .subscriberstation, a two-conductor line connectingthe subscriber station with the telephone exchange; a pair of telegraph channels superimp sed on the two conductors respectively of said line, means for accomplishing svvitchhook Y signalling operations from the substation to the ex change over one of the telegraph'channels, a pair of telegraph stations, and a circuit between saidtelegraph stations including .the other of said 10 telegraph channels. Y 1

2. In combinatioma telephone exchange and a telephone substation, 'a two-conductor line extending from the telephone exchange to the substation, a metallic channel established over; said' l line for the passage of voice currentsthereover from the substation to the exchange,a groundreturn direct-current signal channel superimposed on one of the conductors of said line and extending between the substation and the exchange, a pair of telegraph stations, and a ground-return"telegraph channel superimposed on the other conductor of said lineand extending between said stations.

3. Incombination, atelephone exchange: and a substation set interconnected by a two conductor line, means for transmitting voicecurrentstoand from said substation over a metallic-circuit including the two conductors of said line; means for transmitting ringing current from the exchange to thesubstation over one-conductor 01 r the line and the return circuit separate from the other conductor thereof, meansfor transmitting signal impulses'from the substation to the .ex-

change over the above mentioned conductor used for the transmissionof ringing current and the said separate return conductor, a pair of telegraph stations, and means for transmitting telegraph signals between said stations byway of the other conductor of said line and a separate ground return circuit, and means i'or preventing mutual interference between the; several, operations set V forth. M 

